net: fec: ptp: avoid register access when ipg clock is disabled

BugLink: https://bugs.launchpad.net/bugs/1923220

[ Upstream commit 6a4d723 ]

When accessing the timecounter register on an i.MX8MQ the kernel hangs.
This is only the case when the interface is down. This can be reproduced
by reading with 'phc_ctrl eth0 get'.

Like described in the change in 91c0d98
the igp clock is disabled when the interface is down and leads to a
system hang.

So we check if the ptp clock status before reading the timecounter
register.

Signed-off-by: Heiko Thiery <[email protected]>
Acked-by: Richard Cochran <[email protected]>
Link: https://lore.kernel.org/r/[email protected]
Signed-off-by: Jakub Kicinski <[email protected]>
Signed-off-by: Sasha Levin <[email protected]>
Signed-off-by: Kamal Mostafa <[email protected]>
Signed-off-by: Stefan Bader <[email protected]>

Author: hthiery

drivers/net/ethernet/freescale/fec_ptp.c

@@ -382,9 +382,16 @@ static int fec_ptp_gettime(struct ptp_clock_info *ptp, struct timespec64 *ts)
 	u64 ns;
 	unsigned long flags;
 
+	mutex_lock(&adapter->ptp_clk_mutex);
+	/* Check the ptp clock */
+	if (!adapter->ptp_clk_on) {
+		mutex_unlock(&adapter->ptp_clk_mutex);
+		return -EINVAL;
+	}
 	spin_lock_irqsave(&adapter->tmreg_lock, flags);
 	ns = timecounter_read(&adapter->tc);
 	spin_unlock_irqrestore(&adapter->tmreg_lock, flags);
+	mutex_unlock(&adapter->ptp_clk_mutex);
 
 	*ts = ns_to_timespec64(ns);